U.S. patent number 9,478,414 [Application Number 14/498,036] was granted by the patent office on 2016-10-25 for method for hydrophobization of surface of silicon-containing film by ald.
This patent grant is currently assigned to ASM IP Holding B.V.. The grantee listed for this patent is ASM IP Holding B.V.. Invention is credited to Dai Ishikawa, Akiko Kobayashi, Kiyohiro Matsushita, Akinori Nakano.
United States Patent |
9,478,414 |
Kobayashi , et al. |
October 25, 2016 |
Method for hydrophobization of surface of silicon-containing film
by ALD
Abstract
A method is for hydrophobization of a surface of a
silicon-containing film by atomic layer deposition (ALD), wherein
the surface is subjected to atmospheric exposure. The method
includes: (i) providing a substrate with a silicon-containing film
formed thereon; and (ii) forming on a surface of the
silicon-containing film a hydrophobic atomic layer as a protective
layer subjected to atmospheric exposure, by exposing the surface to
a silicon-containing treating gas without exciting the gas. The
treating gas is capable of being chemisorbed on the surface to form
a hydrophobic atomic layer thereon.
Inventors: |
Kobayashi; Akiko (Tokyo,
JP), Nakano; Akinori (Tokyo, JP), Ishikawa;
Dai (Ome, JP), Matsushita; Kiyohiro (Fuchu,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
ASM IP Holding B.V. |
Almere |
N/A |
NL |
|
|
Assignee: |
ASM IP Holding B.V. (Almere,
NL)
|
Family
ID: |
55585234 |
Appl.
No.: |
14/498,036 |
Filed: |
September 26, 2014 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20160093485 A1 |
Mar 31, 2016 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
21/0228 (20130101); C23C 16/56 (20130101); H01L
21/02359 (20130101); C23C 16/45542 (20130101); H01L
21/02164 (20130101); H01L 21/02362 (20130101); H01L
21/02274 (20130101); H01L 21/3105 (20130101); H01L
21/02126 (20130101); H01L 21/0234 (20130101) |
Current International
Class: |
H01L
21/02 (20060101); H01L 21/3105 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Article by Akiko Kobayshi, Naoto Tsuji, Atsuki Fukazawa and
Nobuyoshi Kobayashi, entitled "Temperature Dependence of SiO2 Film
Growth with Plasma-Enhanced Atomic Layer Deposition," regarding
Thin Solid Films, published by Elsevier in the International
Journal on the Science and Technology of Condensed Matter, in vol.
520, No. 11, (2012), pp. 3994-3998. cited by applicant.
|
Primary Examiner: Tran; Tony
Attorney, Agent or Firm: Snell & Wilmer LLP
Claims
We claim:
1. A method for repairing process-related damage of a
silicon-containing dielectric film formed on a substrate caused by
processing the dielectric film comprises: (i) providing the
silicon-containing dielectric film damaged by the processing of the
dielectric film; (ii) forming a pore-sealing film on a surface of
the damaged dielectric film by plasma-assisted deposition, said
pore-sealing film being constituted by SiO or SiOC and deposited
using an oxygen-containing plasma; and (iii) forming a hydrophobic
atomic layer on a surface of the pore-sealing film by exposing the
surface to a silicon-containing treating gas without exciting the
gas throughout step (iii) so as to chemisorb the gas on the
surface, wherein steps (ii) and (iii) are continuously conducted
without interruption in sequence, wherein the dielectric film has a
first dielectric constant (k1) before the processing, the damaged
dielectric film has a second dielectric constant (k2), the
pore-sealed dielectric film has a third dielectric constant (k3),
and the surface-hydrophobization treated dielectric film has a
fourth dielectric constant (k4), wherein k1.ltoreq.k4<k3<k2;
wherein a recovery rate ((k2-k4)/(k2-k1).times.100) is more than
50%, and an intermediate recovery rate ((k3-k4)/(k3-k1).times.100)
is no more than 50%; wherein the treating gas has a single Si--N
bond and at least one Si--CxHy (x and y represent integers); and
wherein the hydrophobic atomic layer has a contact angle against
water of about 80.degree. or higher.
2. The method according to claim 1, wherein in step (ii), the
plasma-assisted deposition is plasma enhanced atomic layer
deposition (PEALD) using a silicon-containing gas having a single
Si--N bond and at least one Si-A bond in its molecule where A
represents H or CxHy (x and y represent integers).
3. The method according to claim 1, wherein the silicon-containing
gas in step (ii) is the same as the treating gas in step (iii).
4. The method according to claim 1, wherein the oxygen-containing
plasma in step (ii) is an oxygen plasma.
5. The method according to claim 4, wherein an inert gas and an
oxygen gas are continuously and constantly supplied throughout
steps (ii) and (iii).
6. The method according to claim 4, wherein an inert gas and an
oxygen gas are not supplied during step (iii).
Description
BACKGROUND
1. Field of the Invention
The present invention generally relates to a method for repairing
process-related damage of a dielectric film by cyclic processes,
particularly to a method for hydrophobization of a surface of a
silicon-containing film by atomic layer deposition (ALD).
2. Description of the Related Art
Dielectric films are indispensable to increasing processing speed
of semiconductor devices and lowering power consumption of the
devices. Dielectric films are susceptible to damage during their
manufacturing processes, thereby increasing dielectric constants
and/or leakage currents. Such process-related damage includes
damage caused by dry etching and plasma ashing, and washing with
chemicals, and physical damage by chemical mechanical planarization
(CMP), etc. Particularly, in advanced devices, dielectric films are
porous and have low dielectric constant values. Such porous low-k
films are highly susceptible to damage during an etching process
for patterning or the like, and when the films are damaged, the
dielectric constant values increase. In order to recover the
dielectric constant values, restoration of the damaged porous
surface is necessary. Further, before depositing a barrier metal or
the like, pores of the porous surface must be sealed for inhibiting
diffusion of the barrier metal. Thus, after the patterning of the
dielectric film but before deposition of a barrier metal thereon,
restoration and pore-sealing are necessary.
In order to repair such process-related damage of the dielectric
films, U.S. Pat. No. 7,851,232 and U.S. Patent Application
Publication No. 2011/0159202, for example, disclose repairing
damage by UV-excited reaction using a gas containing carbon.
However, although damaged surfaces can be restored to a certain
degree by the above methods using a hydrocarbon film, restoration
is insufficient depending on the degree of damage. Further, a
hydrocarbon film can seal pores of the damaged surfaces, but the
hydrocarbon film does not have sufficient barrier function as a
pore-sealing film against a barrier metal although it can inhibit
diffusion of chemicals such as toluene to a certain degree.
Further, a surface of a pore-sealing film or other a
silicon-containing film is often subjected to atmospheric exposure,
and moisture adsorption occurs on the surface and moisture is
diffused through the pore-sealing film and reaches an underlying
film such as a low-k film, increasing a dielectric constant of the
low-k film.
Any discussion of problems and solutions involved in the related
art has been included in this disclosure solely for the purposes of
providing a context for the present invention, and should not be
taken as an admission that any or all of the discussion were known
at the time the invention was made.
SUMMARY
In some embodiments of the present invention which can solve at
least one of the above-addressed problems, in a method where a SiO
or SiOC film is deposited on a low-k film by atomic layer
deposition (ALD) using a silylation compound, a material which is
capable of rendering a surface of the SiO or SiOC film hydrophobic
when the material is adsorbed onto the surface is introduced to the
surface by ALD using a silicon-containing material as a last step
of the deposition treatment.
In some embodiments, the silicon-containing material has a single
Si--N bond and at least one Si--CxHy bond or Si--H bond in its
molecule. In some embodiments, the silicon-containing material is
selected from the group consisting of dimethylaminotrimethylsilane
(DMATMS), isopropylaminotrimethylsilane,
dimethylaminotrimethylsilane, dimethylaminotriethylsilane,
2-picolylaminotrimethylsilane, hexamethyldisilazane (HMDS), and
tetramethyldisilazane (TMDS).
In some embodiments, the silicon-containing material is the same
material used for depositing the SiO or SiOC film.
In some embodiments, the SiO or SiOC film is a pore-sealing film
formed by plasma-enhanced atomic layer deposition (PEALD). In some
embodiments, the PEALD comprises cycles, each cycle comprising
supplying an ALD material, purging the material, and applying RF
power. In some embodiments, when applying RF power,
oxygen-containing gas such as O.sub.2, NO.sub.2, and/or CO.sub.2 is
introduced for generating a plasma. In some embodiments, RF power
is applied at 100 W or less for 3 seconds or less for a 300-mm
wafer.
For purposes of summarizing aspects of the invention and the
advantages achieved over the related art, certain objects and
advantages of the invention are described in this disclosure. Of
course, it is to be understood that not necessarily all such
objects or advantages may be achieved in accordance with any
particular embodiment of the invention. Thus, for example, those
skilled in the art will recognize that the invention may be
embodied or carried out in a manner that achieves or optimizes one
advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught
or suggested herein.
Further aspects, features and advantages of this invention will
become apparent from the detailed description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of this invention will now be described
with reference to the drawings of preferred embodiments which are
intended to illustrate and not to limit the invention. The drawings
are oversimplified for illustrative purposes and are not
necessarily to scale.
FIG. 1 is a schematic representation of a PEALD apparatus for
depositing a pore-sealing film on a dielectric film usable in an
embodiment of the present invention.
FIG. 2 illustrates a process sequence of a pore-sealing cycle and a
surface-hydrophobization step according to an embodiment of the
present invention.
FIG. 3 illustrates a process sequence of a pore-sealing cycle and a
surface-hydrophobization step according to another embodiment of
the present invention.
FIG. 4 illustrates a process sequence of a pore-sealing cycle and a
surface-hydrophobization step according to still another embodiment
of the present invention.
FIG. 5 is a graph showing the relationship between contact angle
(.degree.) and exposed time (sec) according to embodiments of the
present invention.
DETAILED DESCRIPTION
In this disclosure, "gas" may include vaporized solid and/or liquid
and may be constituted by a single gas or a mixture of gases. In
this disclosure, "film" may refer to a fixed layer (fixed by using,
e.g., active species) which continuously extends in a direction
perpendicular to a thickness direction and can grow or can
accumulate in the thickness direction beyond a thickness of one
atomic layer, "layer" may refer to a structure having a certain
thickness formed on a surface, and "monolayer" may refer to a layer
having a thickness of substantially or nearly one atomic layer or a
layer formed by chemical saturation adsorption which may be
constituted partially by more than one atomic layer. In some
embodiments, a "monolayer" may be formed by a step of adsorption of
a precursor on a surface in one cycle of atomic layer deposition
(ALD), and the monolayer may not be a film but may be converted or
fixed to a monolayer film by a step of surface reaction with
reactive species created by, e.g., a plasma or heat. For example, a
"monolayer", a plurality of which constitute a pore-sealing film or
the like, is a self-assembled layer of molecules having a molecular
size of, for example, about 0.1 nm to about 0.3 nm, which molecules
are adsorbed in pores with a pore size of, for example, 1 to 3 nm
of a damaged low-k film and aligned along with OH group terminals
present in the pores. Also, for example, a "monolayer" constituting
a hydrophobic atomic layer formed on a pore-sealing film or the
like is a self-assembled layer of molecules having a molecular size
of, for example, about 0.1 nm to about 0.3 nm, which molecules are
adsorbed on a surface of the pore-sealing film or the like and
aligned along with OH group terminals present in the surface. A
film may be constituted by a discrete single film having certain
characteristics or multiple films, and a boundary between adjacent
films may or may not be clear and may be established based on
physical, chemical, and/or any other characteristics, formation
processes or sequence, and/or functions or purposes of the adjacent
films. The term "constituted by" refers to "comprising",
"consisting essentially of", or "consisting of" in some
embodiments.
In this disclosure, the thickness of a film or layer refers to an
average thickness of the film or layer as measured when a film or
layer is formed under the same process conditions on a flat
surface, which average thickness is determined by measuring a
thickness of the film or layer at randomly selected multiple points
of the film or layer. In this disclosure, an article "a" or "an"
refers to a species or a genus including multiple species. Further,
in this disclosure, any two numbers of a variable can constitute a
workable range of the variable as the workable range can be
determined based on routine work, and any ranges indicated may
include or exclude the endpoints. Additionally, any values of
variables indicated may refer to precise values or approximate
values and include equivalents, and may refer to average, median,
representative, majority, etc. in some embodiments. In this
disclosure, any defined meanings do not necessarily exclude
ordinary and customary meanings in some embodiments.
In the present disclosure where conditions and/or structures are
not specified, the skilled artisan in the art can readily provide
such conditions and/or structures, in view of the present
disclosure, as a matter of routine experimentation. In all of the
disclosed embodiments, any element used in an embodiment can be
replaced with any elements equivalent thereto, including those
explicitly, necessarily, or inherently disclosed herein, for the
intended purposes. Further, the present invention can equally be
applied to apparatuses and methods.
Some embodiments of the present invention provide a method for
hydrophobization of a surface of a silicon-containing film by
atomic layer deposition (ALD), said surface being subjected to
atmospheric exposure, said method comprising: (i) providing a
substrate with a silicon-containing film formed thereon; and (ii)
forming on a surface of the silicon-containing film a hydrophobic
atomic layer as a protective layer subjected to atmospheric
exposure, by exposing the surface to a silicon-containing treating
gas without exciting the gas, said treating gas being capable of
being chemisorbed on the surface to form a hydrophobic atomic layer
thereon. Since ALD is a self-limiting adsorption reaction process,
the amount of deposited precursor molecules is determined by the
number of reactive surface sites and is independent of the
precursor exposure after saturation, and a supply of the precursor
is such that the reactive surface sites are saturated thereby per
cycle. "Chemisorption" refers to chemical saturation adsorption
which is a kind of adsorption which involves a chemical reaction
between the surface and the adsorbate, without exciting the
adsorbate. In some embodiments, the "hydrophobic atomic layer" is a
monolayer which obtains hydrophobic property through the
chemisorption process. By forming the hydrophobic atomic layer as a
protective layer on the surface of the silicon-containing film, the
surface can effectively be protected from moisture, inhibiting
moisture diffusion through the film and inhibiting an increase of
OH groups in an underlying film such as a low-k film. As a result
of inhibiting an increase of OH groups, an increase of dielectric
constant of the low-k film can effectively be inhibited.
In some embodiments, the hydrophobic atomic layer is formed by
chemical saturation adsorption, wherein the thickness of the layer
is equivalent to a thickness of one atomic layer constituted by
molecules of the treating gas or more but is less than about 1.0
nm, typically less than about 0.5 nm, e.g., about 0.1 nm to about
0.3 nm. In some embodiments, the hydrophobic atomic layer has a
contact angle against water of about 80.degree. or higher.
The k-value (dielectric constant) of a low-k film increases when
the number of OH groups present in pores of the low-k film
increases in the film. When a pore-sealing film is deposited on the
low-k film by ALD and closes the pores, as a first step, a material
for the pore-sealing film is adsorbed at adsorption sites present
on a surface of the low-k film. For example, when an aminosilane
material is used, an amine group thereof undergoes substitution
reaction with an OH group, chemisorbing the aminosilane material on
the surface of the low-k film. The chemisorbed material becomes
hydrophilic as a result of reaction between the chemisorbed
material and an oxidizing gas, forming a SiO film on the low-k
film. Thus, the resultant SiO film formed on the low-k film by ALD
has a hydrophilic surface, and when the surface is exposed to the
atmosphere, moisture is adsorbed on the surface and diffused
through the SiO film, increasing OH groups in the low-k film and
thus increasing the k-value. However, by treating the surface of
the pore-sealing film using a material which is capable of
rendering its surface hydrophobic, as a last step added to the ALD
process of the pore-sealing film (e.g., breaking a vacuum after the
last step), a hydrophobic atomic layer is formed on the surface of
the pore-sealing film, and moisture adsorption from the surface of
the pore-sealing film can effectively be inhibited. Further,
additionally, by using a material which is capable of rendering a
surface of a low-k film hydrophobic when a pore-sealing film is
deposited by ALD, not only the surface of the low-k film but also
the inside pores which are exposed to the material can be
hydrophobic.
Additionally, a pore-sealing film formed by PEALD and constituted
by SiO has at least the following advantages as compared with a
pore-sealing film formed by PEALD and constituted by SiCN or the
like. First, the SiO pore-sealing film has an excellent
conformality, e.g., about 85% or higher or about 90% or higher, and
has an excellent GPC (growth rate per cycle), e.g., about 0.06
nm/cycle or higher or about 0.1 nm/cycle or higher. Further, in
some embodiments, a SiO pore-sealing film can be formed using a
suitable precursor without using a catalyst such as a B- or
Zr-based catalyst.
In some embodiments, the material for the hydrophobic atomic layer
and the material for the pore-sealing film are the same, and the
step of forming the pore-sealing film and the step of forming the
hydrophobic atomic layer are continuously conducted. In the above,
"continuously" refers to without breaking a vacuum, without
interruption as a timeline, without changing treatment conditions,
immediately thereafter, as a next step, or without a discrete
physical or chemical boundary between two structures in some
embodiments. In some embodiments, an inert gas and a reactant gas
for forming the pore-sealing film are continuously and constantly
supplied throughout the steps of forming the pore-sealing film and
the hydrophobic atomic layer. In some embodiments, an inert gas and
a reactant gas for forming the pore-sealing film are not supplied
during the step of forming the hydrophobic atomic layer. The above
embodiments can also be applied to use of a silicon-containing film
other than the pore-sealing film.
The silicon-containing film, on a surface of which the hydrophobic
atomic layer is formed, need not be a pore-sealing film but can be
any suitable film which is benefited by hydrophobization of its
surface. For example, the silicon-containing film is a low-k film
with or without a pore-sealing film.
In some embodiments, the treating gas has a single Si--N bond and
at least one Si-A bond in its molecule where A represents H or CxHy
(x and y represent integers). For chemisorption of the treating
gas, one Si--N bond is sufficient. A Si--N bond is easily subjected
to substitution reaction with an OH group. If the treating gas has
two or more Si--N bonds, a Si--N bond or Si--N bonds which is/are
not used for or do/does not contribute to chemisorption remain(s)
on the surface of the hydrophobic atomic layer. The remaining Si--N
bond(s) contribute(s) to moisture adsorption on the surface of the
hydrophobic atomic layer. The Si-A bond renders the surface
hydrophobic, and a Si--CH.sub.3 bond provides greater hydrophobic
effect than a Si--H bond. In some embodiments, the treating gas has
a single Si--N bond, and at least one Si--CxHy bond (e.g., two,
three, or four Si--CxHy bonds such as S--CH.sub.3 bonds), and need
not have a Si--H bond.
In some embodiments, the treating gas is a gas constituted by at
least one compound selected from the group consisting of
dimethylaminotrimethylsilane (DMATMS),
isopropylaminotrimethylsilane, dimethylaminotrimethylsilane,
dimethylaminotriethylsilane, 2-picolylaminotrimethylsilane,
hexamethyldisilazane (HMDS), and tetramethyldisilazane (TMDS).
In some embodiments, the silicon-containing film has a pore-sealing
film formed as a top layer, and the step of providing the substrate
comprises a step of depositing the pore-sealing film by
plasma-enhanced atomic layer deposition (PEALD). In some
embodiments, the pore-sealing film is deposited using a
silicon-containing gas which is identical to the treating gas. In
some embodiments, the pore-sealing film is deposited using an
oxygen plasma. In some embodiments, the oxygen plasma is generated
by supplying a gas containing oxygen and applying RF power to the
gas. In some embodiments, the thickness of the pore-sealing film is
in a range of about 0.5 nm to about 1.5 nm, depending on the pore
size. When the pore size is about 1 nm, e.g., a k-value is about
2.3, a pore-sealing film having a thickness of about 0.5 nm to
about 1.5 nm can effectively function as a chemical
diffusion-blocking layer, whereas when the pore size is about 3 nm,
e.g., a k-value is about 2.0, a pore-sealing film having a
thickness of about 1.0 nm to about 1.5 nm can effectively function
as a chemical diffusion-blocking layer. In some embodiments, the
pore-sealing film is constituted by SiO, and in other embodiments,
the pore-sealing film is constituted by SiOC.
In some embodiments, the silicon-containing film is a low-k film
which has been damaged in processes. Such process-related damage of
a low-k film may be any damage caused by processing the low-k film,
such as plasma ashing, plasma etching, wet and dry cleaning, etc.,
resulting in a substantial increase of dielectric constant of a
low-k film such as SiO, SiCO, SiN, SiCN, SiC, or other
silicon-based multi-element materials. The "substantial increase"
refers to at least 10%, 20%, or 30%, in some embodiments.
Typically, the damaged surface of the low-k film develops numerous
pores, and is terminated by OH groups. The low-k film includes, but
is not limited to, low-k films constituted by SiO, or boron-based
multi-element materials such as borozine, or multi-element
hydrocarbon materials, etc., having a dielectric constant of about
1.9 to 5.0, typically about 2.1 to 3.0, preferably less than 2.5.
In some embodiments, the low-k film is formed in trenches or holes
including side walls and bottom surfaces, and/or flat surfaces, by
plasma-enhanced CVD, thermal CVD, cyclic CVD, plasma-enhanced ALD,
thermal ALD, radical-enhanced ALD, or any other thin film
deposition methods. Typically, the thickness of the low-k film is
in a range of about 50 nm to about 500 nm (a desired film thickness
can be selected as deemed appropriate according to the application
and purpose of film, etc.).
In some embodiments, the low-k film is a porous low-k film or
extreme low-k film (ELK film) having properties shown in Table 1
below.
TABLE-US-00001 TABLE 1 Porous low-k film properties Dielectric
Constant (k) .ltoreq.2.3 Refractive Index (at 633 nm) .ltoreq.1.40
Porosity (%) .gtoreq.30% Pore Diameter (nm) .ltoreq.1 nm Elastic
Modulus (GPa) .ltoreq.6.5 GPa
In some embodiments, a pore-sealing film is formed by ALD on the
low-k film to alleviate the process-related damage. For example, in
the pore-sealing step, the pore-sealing conditions shown in Table 2
are used. Since ALD is a self-limiting adsorption reaction process,
the number of deposited precursor molecules is determined by the
number of reactive surface sites and is independent of the
precursor exposure after saturation, and a supply of the precursor
is such that the reactive surface sites are saturated thereby per
cycle.
TABLE-US-00002 TABLE 2 (the numbers are approximate) Pore-sealing
conditions Substrate temperature 25 to 500.degree. C. (preferably
50 to 400.degree. C.) Pressure 50 to 1300 Pa (preferably 100 to 800
Pa) Reactant O.sub.2, NO.sub.2, CO.sub.2 Flow rate of reactant 100
to 5000 sccm (continuous) (preferably 200 to 1000 sccm) Dilution
gas (rare gas) He, Ar Flow rate of dilution gas 50 to 3000 sccm
(continuous) (preferably 100 to 2000 sccm) Precursor
dimethylaminotrimethylsilane (DMATMS),
isopropylaminotrimethylsilane, dimethylaminotrimethylsilane,
dimethylaminotriethylsilane, 2- picolylaminotrimethylsilane,
hexamethyldisilazane (HMDS), and/or tetramethyldisilazane (TMDS)
Flow rate of precursor 10 to 2000 sccm (including carrier gas)
(preferably 10 to 500 sccm) Precursor pulse (supply 0.1 to 3 sec
(preferably 0.1 to 1 sec) time of the gas) Purge upon the precursor
pulse 0.5 to 10 sec (preferably 0.5 to 5 sec) RF power (13.56 MHz)
20 to 10 W (preferably 30 to 70 W) for a 300 mm wafer RF power
pulse 0.1 to 3 sec (preferably 0.3 to 1 sec) Purge upon the RF
power pulse 0 to 3 sec (preferably 0 to 0.5 sec) Number of cycles
repeated 3 to 20 (preferably 5 to 10) for pore size of 1 nm; 8 to
30 (preferably 10 to 20) for pore size of 3 nm Thickness of film
0.5 to 1 nm (preferably 1 to 2 nm)
In some embodiments, a hydrophobic atomic layer is formed by ALD on
the pore-sealing film or other low-k film to further alleviating
the process-related damage. For example, in the
surface-hydrophobization step (i.e., the hydrophobic atomic layer
deposition step), the conditions shown in Table 3 are used. Since
ALD is a self-limiting adsorption reaction process, the number of
deposited precursor molecules is determined by the number of
reactive surface sites (OH groups) and is independent of the
precursor exposure after saturation, and a supply of the precursor
is such that the reactive surface sites are saturated by one
cycle.
TABLE-US-00003 TABLE 3 (the numbers are approximate)
Surface-hydrophobization conditions Precursor
dimethylaminotrimethylsilane (DMATMS),
isopropylaminotrimethylsilane, dimethylaminotrimethylsilane,
dimethylaminotriethylsilane, 2- picolylaminotrimethylsilane,
hexamethyldisilazane (HMDS), and/or tetramethyldisilazane (TMDS)
Flow rate of precursor 2 to 900 sccm (preferably 4 to 200 sccm,
(including carrier gas) e.g., 10 to 100 sccm) Precursor pulse
(supply 0.1 to 600 sec (preferably 1 to 300 sec, time of the gas)
e.g., 30 to 120 sec) Purge upon the 0.5 to 600 sec (preferably 1 to
300 sec, precursor pulse e.g., 30 to 120 sec)
The other conditions which are not indicated above but are
necessary for surface-hydrophobization, such as temperature and
pressure, can be unchanged from those shown in Table 2 (note that
the hydrophobic atomic layer deposition does not use RF power). The
supply of the precursor need not be controlled based on the flow
rate, but can be controlled by gas pressure control based on vapor
pressure of the precursor. When the vapor pressure of the precursor
is low, the flow is adjusted by controlling the temperature such
that the vapor pressure can be set at 100 Pa or higher, whereas
when the vapor pressure of the precursor is high, an orifice is
provided downstream of a bottle (containing a mixture of liquid and
vapor of the precursor) to reduce the flow. Accordingly, the flow
rate, supply time, and purge are modified. A skilled artisan can
readily operate the ALD process based on the description disclosed
herein as a matter of routine work.
In the surface-hydrophobization step, as long as the partial
pressure of the precursor can be maintained in the reaction
chamber, gases such as a reactant and a dilution gas or the like
need not be supplied, although such an additional gas can be
supplied for operational reasons (e.g., a reactant and a dilution
gas can be continuously supplied as shown in Table 2 throughout the
hydrophobic atomic layer deposition step for avoiding pressure
fluctuation).
FIG. 2 illustrates a process sequence of a pore-sealing cycle and a
surface-hydrophobization step according to an embodiment of the
present invention. Period (a) is an initial step where a reactant
gas (e.g., O.sub.2) and a dilution gas (e.g., Ar) are supplied to a
reaction chamber, and then, a precursor is supplied to the reaction
chamber before period (b) starts, so that a surface of a wafer is
fully saturated with the precursor. Period (b) is a pore-sealing
film deposition cycle by ALD where the reactant gas and the
dilution gas are continuously supplied to the reaction chamber, and
the precursor is also supplied in a pulse, followed by purging of
the reaction chamber to remove a non-adsorbed precursor from the
surface of a substrate, and then, RF power is applied in a pulse to
the reaction chamber to generate a plasma (an oxygen plasma in this
sequence) to fix the adsorbed precursor on the substrate, thereby
forming a fixed monolayer on the substrate, followed by purging of
the reaction chamber to remove a non-reacted product from the
surface of the substrate. This cycle is repeated until a
pore-sealing film with a desired thickness is achieved. During the
purging step, the reactant gas and the dilution gas function as a
purge gas. Alternatively, a different purge gas can be supplied in
a pulse for purging. Period (c) is a hydrophobization step where
the reactant gas and the dilution gas are continuously supplied to
avoid pressure fluctuation in the reaction chamber, and the
precursor is supplied in a pulse so as to adsorb the precursor on
the substrate, thereby forming an unfixed or chemisorbed monolayer,
followed by purging of the reaction chamber by the dilution gas to
remove a non-chemisorbed precursor from the surface of the
substrate. In period (c), no RF power or other means for exciting
the monolayer is applied, and the chemisorbed monolayer remains
unfixed and constitutes an uppermost layer which is exposed to the
atmosphere or a moisture-containing environment, i.e., period (c)
is conducted once as the last step of the deposition process of the
pore-sealing film. In some embodiments, period (c) is conducted
more than once (e.g., twice) in order to ensure that a complete,
continuous monolayer without significant holes is formed by
chemisorption.
FIG. 3 illustrates a process sequence of a pore-sealing cycle and a
surface-hydrophobization step according to another embodiment of
the present invention. This sequence is the same as the sequence
illustrated in FIG. 2 except that while supplying the precursor in
period (c), no reactant gas or no dilution gas is supplied. Since a
reactant gas and a dilution gas do not contribute to chemisorption
of the precursor to form a hydrophobic atomic layer, these gases
can be stopped while supplying the precursor in period (c),
followed by purging of the reaction chamber by the dilution gas to
remove a non-chemisorbed precursor from the surface of the
substrate.
FIG. 4 illustrates a process sequence of a pore-sealing cycle and a
surface-hydrophobization step according to still another embodiment
of the present invention. This sequence is the same as the sequence
illustrated in FIG. 3 except that in period (a), no precursor is
supplied. The prolonged or extended supply of the precursor only in
the first cycle in period (b) as illustrated in FIG. 3 (i.e., the
supply of the precursor begins before period (b) starts) can ensure
that sufficient chemisorption occurs from the first cycle, but need
not be conducted.
In some embodiments, the reactant gas can be supplied only when RF
power is applied in period (b).
In some embodiments, the precursor used in period (b) and the
precursor used in period (c) are different. However, if both
precursors have a single Si--N bond and at least one Si--H or
Si--CxHy bond, the k-value can be recovered more significantly than
in the case where only the precursor used in period (c) has a
single Si--N bond and at least one Si--H or Si--CxHy bond, since OH
groups can be removed not only from the surface but also from the
inside of pores. In some embodiments, period (b) and period (c) are
performed discontinuously in the same chamber or in different
reaction chambers. However, it is preferable to continuously
conduct the two periods and keep as many process conditions
unchanged as possible, for simpler operation. Further, it is
preferable to treat the exposed surface with a hydrophobic atomic
layer in period (c) before the exposed surface is exposed to the
atmosphere or moisture-containing environment.
In some embodiments, by the surface-hydrophobization step, the
k-value of the silicon-containing film which has been damaged can
be recovered to the original k-value of the silicon-containing film
(which original k-value is a value before being damaged) or a
k-value substantially close to the original k-value (e.g., an
increase can be controlled within about 5% or less or about 10% or
less of the original k-value).
In another aspect of the present invention, a method for repairing
process-related damage of a silicon-containing dielectric film
formed on a substrate caused by processing the dielectric film
comprises: (i) providing the silicon-containing dielectric film
damaged by the processing of the dielectric film; (ii) forming a
pore-sealing film on a surface of the damaged dielectric film by
plasma-assisted deposition, said pore-sealing film being
constituted by SiO or SiOC; and (iii) forming a hydrophobic atomic
layer on a surface of the pore-sealing film by exposing the surface
to a silicon-containing treating gas without exciting the gas so as
to chemisorb the gas on the surface, wherein the dielectric film
has a first dielectric constant (k1) before the processing, the
damaged dielectric film has a second dielectric constant (k2), the
pore-sealed dielectric film has a third dielectric constant (k3),
and the surface-hydrophobization treated dielectric film has a
fourth dielectric constant (k4), wherein k1.ltoreq.k4<k3<k2,
and a recovery rate ((k2-k4)/(k2-k1).times.100) is more than 50%,
e.g., 60% to 90%, and an intermediate recovery rate
((k3-k4)/(k3-k1).times.100) is up to 50%, e.g., 20% to 50%. In the
above, the dielectric constant is a dielectric constant of the
dielectric film provided with, in any, a pore-sealing film and a
hydrophobic atomic layer. For example, the thickness of the
dielectric film is about 200 nm, the thickness of the pore-sealing
film is about 1 nm, and the thickness of the hydrophobic atomic
layer is about 0.5 nm, and thus, the dielectric constant of the
pore-sealing film alone (e.g., k=about 4) does not affect the total
dielectric constant of the dielectric film with the pore-sealing
film. In some embodiments, the pore-sealing film and the
hydrophobic atomic layer can be any of those disclosed herein. In
some embodiments, there is no intervening chemical treatment step
such as a surface-oxidization step between steps (ii) and
(iii).
In some embodiments, in step (ii), the plasma-assisted deposition
is plasma enhanced atomic layer deposition (PEALD) using a
silicon-containing gas having a single Si--N bond and at least one
Si-A bond in its molecule where A represents H or CxHy (x and y
represent integers). In some embodiments, the silicon-containing
gas in step (ii) is the same as the treating gas in step (iii).
Initially, a SiO or SiOC film by PEALD was believed to be
unsuitable as a pore-sealing film because it may further damage the
underlying dielectric film. However, by forming a hydrophobic
atomic layer thereon (especially when the SiO or SiOC pore-sealing
film is formed using a single Si--N bond and at least one Si-A bond
in its molecule where A represents H or CxHy (x and y represent
integers)), the process-related damage can effectively be
recovered. The SiO or SiOC pore-sealing film has advantages such as
high deposition rate (e.g., 0.06 to 0.1 nm/cycle) and high
conformality (at least 85%) as compared with a SiN pore-sealing
film.
In the present disclosure where conditions and/or structures are
not specified, the skilled artisan in the art can readily provide
such conditions and/or structures, in view of the present
disclosure, as a matter of routine experimentation. Also, in the
present disclosure, the numerical values applied in specific
embodiments can be modified by a range of at least .+-.50% in other
embodiments, and the ranges applied in embodiments may include or
exclude the endpoints.
EXAMPLES
FIG. 1 is a schematic representation of a PEALD apparatus for
depositing a pore-sealing film on a dielectric film usable in an
embodiment of the present invention. In this example, by providing
a pair of electrically conductive flat-plate electrodes 4, 2 in
parallel and facing each other in the interior 11 of a reaction
chamber 3, applying HRF power (13.56 MHz or 27 MHz) 5 and LRF power
of 5 MHz or less (400 kHz-500 kHz) (not shown) to one side, and
electrically grounding the other side, a plasma is excited between
the electrodes. A temperature regulator is provided in a lower
stage 2 (the lower electrode), and a temperature of a substrate
placed thereon is kept constant at a given temperature. The upper
electrode 4 serves as a shower plate as well, and a precursor gas
is introduced into the reaction chamber 3 through a gas flow line
23, a pulse flow control valve 31, and the shower plate 4, whereas
a rare gas is introduced into the reaction chamber 3 through a gas
flow line 21 and the shower plate 4. A line for introducing a
reactant gas is omitted (since the precursor is not reactive to an
oxidizing gas without excitation, an oxidizing gas can be supplied
concurrently with the precursor). Additionally, in the reaction
chamber 3, an exhaust pipe 6 is provided, through which gas in the
interior 11 of the reaction chamber 3 is exhausted using a pressure
control valve 16 connected to a vacuum pump 17. Additionally, the
reaction chamber is provided with a seal gas flow controller (not
shown) to introduce seal gas into the interior 11 of the reaction
chamber 3 (a separation plate 15 for separating a reaction zone and
a transfer zone in the interior of the reaction chamber is
provided).
In the examples, the apparatus shown in the schematic diagram of
FIG. 1 was used to form a film. Note that the present invention is
not at all limited to the apparatus shown in this figure and any
other apparatus can be used so long as it can perform PEALD.
Comparative Example 1
1) A Si substrate (300 mm in diameter with patterns having an
aspect ratio of about 4 with a width of about 80 nm) was placed in
the reactor and a Sloane polymer film was formed on the substrate
using Aurora.RTM. X (diethoxymethylsilane; ASM International N.V.)
and Pore Builder.TM. (hydrocarbon for atom transfer radical
polymerization; ASM International N.V.), He, and O.sub.2. The
substrate with the siloxane polymer film was transferred to a UV
reactor and subjected to UV cure, thereby obtaining an ELK film
having a dielectric constant of 2.3.
2) Next, the substrate with the ELK film was transferred to a
reactor for plasma ashing or etching under the conditions shown in
Table 4 below, thereby causing plasma damage to the ELK film. As a
result of the plasma damage, the dielectric constant of the ELK
film increased to 3.0.
TABLE-US-00004 TABLE 4 (the numbers are approximate) Damage
conditions RF frequency 13.56 MHz HRF 60 W Treatment time 24 sec
Substrate temperature 250.degree. C. Pressure 466 Pa He 2000 sccm
O.sub.2 12 sccm Gap between electrodes 8 mm
3) Next, the substrate with the damaged ELK film was transferred to
the reactor illustrated in FIG. 1 for pore-sealing using
bisdiethylaminosilane (BDEAS) under the conditions shown in Table 5
below using the process sequence illustrated in FIG. 2 (except that
no hydrophobization step was performed), thereby obtaining a
pore-sealed ELK film.
TABLE-US-00005 TABLE 5 (the numbers are approximate) Pore-sealing
conditions Substrate temperature 170.degree. C. Pressure 200 Pa
Reactant gas O.sub.2 Flow rate of reactant 100 sccm gas
(continuous) Dilution gas Ar Flow rate of dilution 500 sccm gas
(continuous) Precursor BDEAS Precursor pulse (supply time) 1 sec at
5 sccm Purge upon precursor pulse 1 sec RF frequency 13.56 MHz RF
power 50 W RF power pulse 1 sec Purge upon the RF power pulse 0.5
sec Number of cycles repeated 10 Thickness of pore-sealing film 1
nm
The film was evaluated after the film was exposed to the
atmosphere, and the results are shown in Table 6. The pore-sealed
ELK film did not recover the dielectric constant, and rendered the
exposed surface highly hydrophilic as shown in Table 6. BDEAS has
two Si--H bonds, but no Si--CxHy bond, and two Si--N bonds in its
molecule.
The contact angle against water was measured as follows: a water
drop (0.3 .mu.ml) was dropped on the surface of the substrate at
room temperature (25.degree. C.), and the angle of the drop
relative to the surface of the substrate was measured based on a
photograph taken in a horizontal direction. When the angle is
80.degree. or higher, the surface is considered to be highly
hydrophobic, whereas when the angle is 30.degree. or lower, the
surface is considered to be highly hydrophilic. The conformality
was defined as a ratio of thickness of a film on a sidewall to
thickness of a film on a top surface.
TABLE-US-00006 TABLE 6 (the numbers are approximate) GPC (growth
Conformality Recovered Contact angle per cycle [nm]) (step
coverage) k-value against water Comparative 0.06 to 0.1 90% 3.0
10.degree. Example 1
Example 1
In a manner substantially similar to that in Comparative Example 1,
a damaged ELK film was prepared, which had a dielectric constant of
3.0. The damaged ELK was subjected to the pore-sealing cycles under
the conditions shown in Table 7 using dimethylaminotrimethylsilane
(DMATMS) to obtain a pore-sealed ELK film. Next, the pore-sealed
ELK film was subjected continuously to a hydrophobization step in
the reaction chamber under the conditions shown in Table 8 to treat
the pore-sealed surface of the film with a hydrophobic atomic
layer. The process sequence illustrated in FIG. 2 was used
herein.
TABLE-US-00007 TABLE 7 (the numbers are approximate) Pore-sealing
conditions Substrate temperature 250.degree. C. Pressure 200 Pa
Reactant gas O.sub.2 Flow rate of reactant 30 sccm gas (continuous)
Dilution gas Ar Flow rate of dilution 500 sccm gas (continuous)
Precursor DMATMS Precursor pulse (supply time) 1 sec at 100 sccm
Purge upon precursor pulse 3 sec RF frequency 13.56 MHz RF power 50
W RF power pulse 1 sec Purge upon the RF power pulse 1 sec Number
of cycles repeated 10 Thickness of pore-sealing film 1 nm
TABLE-US-00008 TABLE 8 (the numbers are approximate)
Hydrophobization conditions Precursor DMATMS Precursor supply time
120 sec at 100 sccm Purge upon precursor supply 30 sec
The conditions for the pore-sealing, such as temperature and
precursor flow rate, were slightly different from those in
Comparative Example 1 because the flow of the precursor was
controlled based on the pressure, and the vapor pressure of the
precursor in Example 1 was different from that in Comparative
Example 1. In Table 8, the supply time and flow rate of the
precursor were significantly extended to ensure that the surface of
the pore-sealed film was saturated with the chemisorbed precursor.
However, the supply time and flow rate of the precursor can be
significantly shorter as long as the surface of the pore-sealed
film can be saturated with the chemisorbed precursor.
The film was evaluated after the film was exposed to the
atmosphere, and the results are shown in Table 9. The pore-sealed
ELK film with the hydrophobic atomic layer significantly recovered
the dielectric constant, and rendered the exposed surface highly
hydrophobic as shown in Table 9. DMATMS has one Si--N bond and
three Si--CxHy bonds in its molecule. The surface-treated ELK film
can continuously block moisture adsorption and maintain the
recovered k-value, even when the surface is exposed to the
atmosphere.
TABLE-US-00009 TABLE 9 (the numbers are approximate) GPC (growth
Conformality Recovered Contact angle per cycle [nm]) (step
coverage) k-value against water Example 1 0.06 to 0.1 90% 2.4
90.degree.
Example 2 and Comparative Examples 2, 3, and 4
In a manner substantially similar to that in Comparative Example 1
and Example 1, a damaged ELK film was prepared, which had a
dielectric constant of 2.8 or 2.7 (the k-value before being damaged
was 2.3). The damaged ELK was subjected to the pore-sealing cycles
under the conditions shown in Table 10 using
dimethylaminotrimethylsilane (DMATMS) for Comparative Example 2 and
Example 2, and bisdiethylaminosilane (BDEAS) for Comparative
Examples 3 and 4 to each obtain a pore-sealed ELK film. Next, the
pore-sealed ELK film was subjected continuously to a
surface-treating step in the reaction chamber under the conditions
shown in Table 11 to treat the pore-sealed surface of the film.
TABLE-US-00010 TABLE 10 (the numbers are approximate) Pore-sealing
conditions Substrate temperature 50.degree. C. Pressure 200 Pa
Reactant gas O.sub.2 Flow rate of reactant 30 sccm gas (continuous)
Dilution gas Ar Flow rate of dilution 500 sccm gas (continuous)
Precursor DMATMS or BDEAS Precursor pulse 1 sec at 100 sccm (supply
time) for DMATMS, at 5 sccm for BDEAS Purge upon 3 sec precursor
pulse RF frequency 13.56 MHz RF power 50 W RF power pulse 0.5 sec
Purge upon the 0.5 sec RF power pulse Number of cycles 10 repeated
Thickness of pore- 1 nm sealing film
TABLE-US-00011 TABLE 11 (the numbers are approximate) Comparative
Comparative Comparative Example 2 Example 2 Example 3 Example 4
Precursor DMATMS DMATMS BDEAS BDEAS Precursor 100 sec 120 sec 100
sec 120 sec supply time at 5 sccm at 100 sccm at 5 sccm at 100 sccm
Purge upon 3 sec 30 sec 3 sec 30 sec precursor supply RF power 50 W
None 50 W None RF power 1 sec None 1 sec None pulse
The surface treatment step in each Comparative Examples 2 and 3 was
the extension of the pore-sealing step, i.e., an additional cycle
of the pore-sealing step was repeated, and no separate surface
treatment step was conducted.
Each film was evaluated after the film was exposed to the
atmosphere, and the results are shown in Table 12. The pore-sealed
ELK film with the hydrophobic atomic layer formed from DMATMS in
Example 2 remarkably recovered the dielectric constant (the
recovery rate was 80%), and rendered the exposed surface highly
hydrophobic (a contact angle was 90.degree.) as shown in Table 12.
In contrast, the pore-sealed ELK film with the atomic layer formed
from BDEAS in Comparative Example 4 did not significantly recover
the dielectric constant (the recovery rate was 20%), and the
exposed surface was rendered hydrophilic (the contact angle was
45.degree.) as shown Table 12. Further, the pore-sealed ELK film
without a separate surface treatment step in Comparative Example 2
moderately recovered the dielectric constant (the recovery rate was
40%), but the exposed surface was rendered highly hydrophilic (the
contact angle was 10.degree.) as shown in Table 12, even though the
precursor was the same as in Example 2 (i.e., DMATMS). That is,
when the atomic layer was unfixed, i.e., a chemisorbed monolayer,
the surface could be rendered highly hydrophobic, and when the
atomic layer was fixed, even if the same treating gas was used, the
surface could not be rendered hydrophobic, and the k-value recovery
was not satisfactory. This is because when a SiO film is formed by
ALD as the pore-sealing film was formed in the above examples, the
ALD includes an oxidization cycle where the surface constituted by
SiOC is oxidized, i.e., generating OH groups on the surface and
contributing to an increase of a k-value. In Example 2 or other
embodiments, although the ALD includes an oxidization cycle to form
a pore-sealing film, thereby generating OH groups on the surface,
the subsequent hydrophobization step can replace OH groups with,
e.g., CH.sub.3 groups via the chemisorption process without
excitation, thereby alleviating the process-related damage. In
Comparative Example 3, since no separate surface treatment step was
conducted and BDEAS was used as the treating gas, the k-value was
not recovered (the recovery rate was 0%), and the surface was
highly hydrophilic (the contact angle was 10.degree.). In
Comparative Example 2, because DMATMS was used to form the
pore-sealing film, Si--CH.sub.3 groups present in DMATMS could
remain inside the pores, contributing removal of OH groups from the
pores. Thus, the recovery rate (40%) in Comparative Example 2 was
significantly better than that (0%) in Comparative Example 3,
although the surfaces of both films were hydrophilic (the contact
angle was 10.degree.) since no hydrophobization was performed.
TABLE-US-00012 TABLE 12 Treating Damaged Recovered Recovery Contact
gas k-value k-value rate angle Comparative DMATMS 2.8 2.6 40%
10.degree. Example 2 Example 2 DMATMS 2.8 2.4 80% 90.degree.
Comparative BDEAS 2.8 2.8 0% 10.degree. Example 3 Comparative BDEAS
2.7 2.6 20% 45.degree. Example 4
Example 3
In a manner substantially similar to that in Example 1, a
pore-sealed ELK film was prepared and subjected continuously to a
surface-treating step (hydrophobization step) in the reaction
chamber under conditions which were the same as in Example 1 except
that the gas-exposure time (precursor supply time) varied from 0
sec to 300 sec (i.e., 0, 0.1, 0.5, 1.0, 30, 120, and 300 sec). The
contact angle of each resultant treated surface is shown in FIG. 5.
As shown in FIG. 5, the contact angle was drastically changed
toward a hydrophobic state at a gas-exposure time of 0.5 sec, and
the contact angle reached 80.degree. at a gas-exposure time of 30
sec, i.e., rendering the surface hydrophobic. Thereafter, the
contact angle appeared to reach a plateau in a range of 80.degree.
to 90.degree..
Examples 4 and 5
In a manner substantially similar to that in Example 2, a damaged
ELK film was prepared, and the damaged ELK was subjected to the
pore-sealing cycles (the number of cycles was changed as shown in
Table 13), and then, the pore-sealed ELK film was subjected
continuously to the surface hydrophobization step in the reaction
chamber. The ELK film in Example 4 had an original k-value of 2.3
and a pore size of about 1 nm, and the ELK film in Example 5 had an
original k-value of 2.0 and a pore size of about 3 nm. The ELK
films in Examples 4 and 5 were subjected to a chemical diffusion
test where the substrate was submerged in a liquid chemical
(ethanol) for 5 minutes, and then a cross section of the substrate
was observed to see if the chemical penetrated through the surface
and diffused toward the inside the substrate. The results are shown
in Table 13.
TABLE-US-00013 TABLE 13 Thickness of pore-sealing film Original
(the number of ALD cycles) k-value 0 nm 0.5 nm 1 nm 1.5 nm (pore
size) (0 cycles) (5 cycles) (10 cycles) (15 cycles) Example 4 2.3
(1 nm) x Example 5 2.0 (3 nm) x x --
The symbol "x" represents that diffusion was observed, and the
symbol ".smallcircle." represents that no diffusion was observed.
The thickness of the pore-sealing film was a thickness of a
pore-sealing film which was formed on a flat Si surface under the
same conditions. As shown in Table 13, the surface of the substrate
having a pore size of about 1 nm (with a k-value of 2.3) was
successfully sealed by a pore-sealing film having a thickness of
0.5 nm or higher, whereas the surface of the substrate having a
pore size of about 3 nm (with a k-value of 2.0) was successfully
sealed by a pore-sealing film having a thickness of 1.0 nm or
higher.
Example 6
In this example, the substrate having the pore-sealing film having
a thickness of 1 nm, prepared in Example 4, was subjected to
further film deposition where a TiN film was deposited by ALD as a
barrier film on top of the substrate. Thereafter, the substrate was
analyzed to see if Ti was diffused and migrated into the low-k film
using Backside SIMS (Secondary Ion Mass Spectrometry). It was
confirmed that no Ti diffusion was detected in the low-k film,
indicating that the pore-sealing film functioned as a pore-sealing
film which effectively blocked migration of Ti into the low-k
film.
It will be understood by those of skill in the art that numerous
and various modifications can be made without departing from the
spirit of the present invention. Therefore, it should be clearly
understood that the forms of the present invention are illustrative
only and are not intended to limit the scope of the present
invention.
* * * * *